The invention relates to a spoked wheel of the type including a rim with a plurality of holes for a respective plurality of nipples, and an equal plurality of spokes secured to the rim by means of the nipples.
Wheels of the above-mentioned type are widely used on both pedal cycles and motorcycles. In the latter case in particular, a need has been felt to use pneumatic tires of the tubeless type, without an inner tube.
These tires have the advantage of deflating relatively slowly in case of a puncture and are therefore suited to the high speeds which may occur in the case of motorcycles.
On the other hand, the use of tubeless tires is not compatible with spoked wheels unless these incorporate special characteristics.
A first type of spoked wheel designed for cycle use with tubeless tires provides for the rim to have a double channel. The first channel is formed between the rim and the tire and provides an airtight seal designed to form the inflation chamber of the tire. The second channel, provided with holes, is used for fitting the spoke anchorage devices. Examples of this technical solution are described in U.S. Pat. No. 6,474,746 and US 2003/0025383 A1.
However, this type of wheel is not well suited to motorcycle use since it increases appreciably the mass of the rim in rotation. Moreover, it has been found that in wet conditions water tends to accumulate in the second channel (which is not airtight) with disadvantages such as an increase of the mass in rotation, corrosion phenomena and worse still appreciable wheel imbalance.
Another type of wheel for the fitting of tubeless tires is described in Japanese patent 2003146001, European patent 1209006 and U.S. Pat. No. 4,824,177. In this case, however, external sealing means are used to eliminate the problem of airtightness between the nipple and the rim.
This type of solution provides relatively unreliable sealing which is likely to be damaged if impacts occur.
Moreover, it has been found that a serious sealing problem is caused by relative movement between the rim and the nipple due to the inevitable elastic deformation of the rim during use. This is because there may be axial displacement of the nipple and of the spoke secured to it due to the effect of deformation of the rim by even a few millimetres and, when seals are inserted between the nipple and the rim, it is clear that this may cause pressure losses in the inflation chamber of the tire and may even cause sudden deflation of the tire.